Young and British - the London suicide bombers

The face of terrorism in Britain has changed for ever as police established that the London bomb blitz was carried out by four suicide bombers.

At least three were British-born, from outwardly respectable families of Pakistani origin.

They lived quietly in the Leeds area and none had criminal records.

Their identities emerged after police raided a number of addresses in West Yorkshire, including the dead men's homes.

In one, they found an apparent bomb factory, but the man who made the devices is thought to have fled the country days ago.

Police are trying desperately to discover if other devices have been distributed to would-be attackers.

A car in which the bombers drove south was discovered at Luton railway station.

From there they took a train to King's Cross, where they have been spotted on CCTV film "looking happy and carefree, as if they were going on holiday" said a security source. Shehzad Tanweer, 22, carried his bomb on to the train which was blasted at Aldgate. A keen local cricketer and sports science student, he lived with his parents, who run a fish and chip shop in the Beeston area of Leeds.

A second Leeds man, 30-year-old Mohammed Sadique Khan, who was married, boarded the train which blew up at Edgware Road.

A third man, about whom no details have yet emerged, was on the train which was devastated near Russell Square station.

At 8.50am, the time they had pre-arranged, they detonated their explosives.

The fourth suicide bomber was 19-year-old Hasib Mir Hussain, who lived with his Pakistani-born factory worker parents in a rundown Leeds suburb.

He died almost an hour later, when he triggered his bomb on a number 30 bus in Tavistock Square.

First suicide bombers in Europe

It is the first time suicide bombers have struck in Europe.

A senior anti-terrorist investigator said last night: "This was the most worrying scenario of all.

"The nature of what we are up against has changed completely. We are dealing with people who are prepared to die, who want to become martyrs and we don't know how many more are out there, how many copycats there could be.

"They didn't have to die, they could have carried out the bombing without killing themselves, but they chose to do so. It is a real statement."

Police are trying to discover whether other attacks have been planned and what has happened to the bombmaker, a suspected Al Qaeda expert. They say "considerable expertise" would have been needed to build them.

In previous operations Al Qaeda has been known to 'bring in, bring out' a bombmaker, who will make several devices but be beyond the reach of security forces before any go off.

Police are also seeking to establish whether any of the bombers had been to Pakistan or trained in Al Qaeda camps in Afghanistan.

Confirmation that the bombers were British is vindication for former Scotland Yard chief Lord Stevens, who said at the weekend he believed they would be British-born and bred.

He warned that up to 3,000 British-based men had trained at terror camps and said Al Qaeda recruiters were targeting a new breed of educated, computer-literate terrorists.

As the massive investigation - codenamed Operation Thesis - developed rapidly yesterday, Tony Blair vowed that terrorists would fail in their attempts to shatter the fabric of British society.

"We are determined to bring all those responsible to justice and to ensure our values and way of life remain undiminished," he said.

The extraordinary breakthrough in Britain's biggest ever manhunt followed minute examination of the scenes of the blasts.

Working in horrific conditions amid the carnage deep below ground, forensic experts were able to establish that all the Tube bombers died by recovering distinctive body parts and clothing.

Forensic experts sifting through the bus where 13 people were killed also found parts of the clothes and body of the bomber.

Property and papers relating to the men were also found.

Anti-terrorist officers had always suspected that the terror group had been at Kings Cross as all the bombings were close to the station.

At 8pm on Monday painstaking examination of CCTV from the station paid off.

'Like infantry going off to war

It showed the four men, wearing casual clothes and carrying military-style rucksacks, shortly before 8.30am on Thursday. They were "like infantry going off to war," said a senior security source.

As the pace of the inquiry quickened, Scotland Yard officers and West Yorkshire police launched raids in Leeds and nearby Dewsbury.

Some 500 Leeds residents were evacuated as bomb disposal officers moved in to the suspected bomb factory, removing dozens of packages. A relative of one of the dead men was being held under the Terrorism Act last night.

In Luton, police sealed off the car park and carried out four controlled explosions.

Bomb squad officers later removed what they believed were explosives from the car.

The three Leeds men had left the city on Wednesday in the car, which had been hired by Tanweer. They drove down the M1 to Luton and teamed up with the fourth man.

They spent the night in the Luton area before boarding the 7.40am Thameslink commuter train to London - bizarrely forking out for a pay and display ticket at Luton station.

A woman has told police she saw the men board the train, which made stops at Harpenden and St Albans, arriving at Kings Cross at 8.20am.

The identification of Hussain was helped by his worried mother Maniza, who called police some hours after the blasts to say he had travelled to London "with his mates" but was not answering his mobile.

She gave his name, address and contact details as well as a description of his appearance and clothes.

Detective Assistant Commissioner Peter Clarke, head of Scotland's Yard anti-terrorist branch, confirmed yesterday: "We have found personal documents bearing the names of three of those four men close to the seats of three of the explosions."

While some suicide bombers destroy all evidence of who they are, the fact that the four made a point of carrying identification documents was seen by investigators as a final act of defiance - and intent.